There are known arts for reading a dot pattern printed on the surface of a medium, such as paper, and outputting the data corresponding to such dot pattern.
Several researchers, including the present inventor, have focused on the dot pattern layout theory and proposed different techniques for effective layout of dot patterns.
Along with these efforts, technology for printing dot patterns has become increasingly sophisticated, and this has made it possible today to arrange a dot pattern with much higher densities on a paper surface.
Patent literatures that propose dot pattern reading systems reflecting these advancements include Japanese Patent Domestic Laid-open Publication No. 2003-528387 applied by Anoto AB (Patent literature 1).
The present invention incorporates two prior arts relating to dot patterns:
    PCT/JP03/03162 and PCT/JP03/16763, both by the present inventor (hereinafter referred to as “GRID-1” and “GRID-2,” respectively, for the sake of simplicity).    [Patent Literature 1] Japanese Patent Domestic Laid-open Publication No. 2003-528387